Polyurethane foam

ABSTRACT

This disclosure describes a method of making a polyurethane foam and a method of reducing NVH expected to be experienced by a substrate using the foam. When the foam is subjected to 95% relative humidity for a period of 7 days at a temperature of about 50° C., the foam absorbs an amount of water that is less than about 30% of the weight of the foam.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication No. 60/986,497, filed on Nov. 8, 2007, the entirety of whichis hereby incorporated by reference.

FIELD

The present disclosure relates generally to polyurethane foams, and moreparticularly, to polyurethane foams that are suitable for use asstructural reinforcing, sealing and/or acoustic damping members.

BACKGROUND

During the fabrication of automobiles, trucks, and similar over-the-roadvehicles, many body components present structural members havingcavities that require sealing to prevent the entrance of moisture andcontaminants which can cause corrosion of the body parts. It isgenerally desirable to strengthen the members while maintaining theirlight weight. It is also beneficial to stabilize these members in orderto attenuate and dampen noise and vibrations that would otherwise betransmitted along the length or passage of the cavity. Many of thesecavities are irregular in shape or narrow in size, thus making themdifficult to properly seal.

Polyurethanes are a class of materials that can be used to prepare rigidfoams and are potentially useful for forming the type of reinforcing,sealing, and/or acoustic damping members described above. Polyurethanesare prepared by combining one or more polyols with one or morepolyisocyanates. Commonly used polyisocyanates include aromaticdiisocyanates, such as methylene diphenyl diisocyanate (“MDI”) andtoluene diisocyanate (“TDI”), as well as oligomers or polymers thereof.

Many known polyisocyanates are supplied with significant levels (morethan 20%) of free isocyanate monomer. The reaction temperatures used todrive the polyurethane formation process typically raise the vaporpressure of the unreacted monomer and cause it to volatilize. Due to thetoxicity of certain isocyanate monomers, additional steps are oftentaken to reduce their atmospheric concentration in areas to whichpersonnel are exposed. In some instances, ventilated structures such as“down draft booths” are provided to minimize personnel exposure to thevolatilized monomers. However, providing such ventilated structures canbe costly and difficult. Thus, a need has arisen for a polyurethane foamthat addresses the foregoing issues.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a process used to prepare and apply a polyurethane foamto a cavity of a structure; and

FIG. 2 depicts the variation of volatilized methylene diphenyldiisocyanate as a function of both reaction temperature and the ratio ofisocyanate equivalents to hydroxyl equivalents in a polyurethaneformulation.

DETAILED DESCRIPTION

Described herein are polyurethane compositions that are particularlysuited for preparing rigid foams. While the rigid foams have a number ofapplications, one application of particular interest involves sealingand structural reinforcing members used to seal cavities betweenstructural members of mechanical devices or structures, includingcavities formed in various locations within vehicle bodies. Anotherapplication of interest involves acoustic damping foams that dampenacoustic vibrations to reduce the noise, vibration, and harshness(“NVH”) experienced by vehicle occupants. In such applications, it isdesirable to use foam of relatively low density, low water absorption,and high sag resistance. It is also desirable to apply the foam suchthat it forms a tight seal and/or closely follows the contours of thecavity being sealed or the substrate being foamed.

The compositions described herein provide a polymeric foam that issuitable for sealing, reinforcing, and/or acoustic damping applicationswhile advantageously reducing the amount of free, unreacted isocyanatemonomer that is volatilized. In certain embodiments, the foams arereferred to as “booth free” foams because they can be applied withoutthe use of down draft booths. The polyols and polyisocyanates tend toreact quickly. As a result, in certain embodiments, the reactants usedto prepare the foam are provided in liquid form and are concurrentlymixed and applied to the cavity or substrate of interest, causing therapid formation of foam and sealing of the cavity or foaming of thesubstrate.

The polymeric foam compositions described herein generally comprise afirst component that includes at least one polyol, and a secondcomponent that includes at least one polyisocyanate. A blowing agent isalso generally provided. The blowing agent causes the formation of gaswhich then creates the cells in the polyurethane that define the foamedstructure. In a preferred formulation, the blowing agent is water, whichreacts with the polyisocyanate to produce carbon dioxide gas. However,other blowing agents may be used, either alone or in combination withwater. The polyurethane compositions may also include cross-linkers,chain extenders, catalysts, cell openers, additives, and surfactants.

As is known to those skilled in the art, polyurethane compositions canbe characterized by an index that is defined as the ratio of theequivalents of isocyanate groups to the equivalents of hydroxyl groups:

$\begin{matrix}{{Index} = \frac{{number}\mspace{14mu} {of}\mspace{14mu} {equivalents}\mspace{14mu} {of}{\mspace{11mu} \;}{isocyanate}\mspace{14mu} {groups}}{\begin{matrix}{{number}\mspace{14mu} {of}\mspace{14mu} {equivalents}{\mspace{11mu} \;}{of}} \\{{hydroxyl}\mspace{14mu} {groups}\mspace{14mu} \left( {{including}\mspace{14mu} {water}} \right)}\end{matrix}}} & (1)\end{matrix}$

In equation (1), the number of isocyanate equivalents is based on allisocyanate-containing compounds, including isocyanate functional groupsthat are present as free isocyanate-containing monomers and asfunctional groups on polymeric or oligomeric polyisocyanates. Similarly,the number of equivalents of hydroxyl groups is based on all compoundsthat contain hydroxyl groups, including water. As will be seen below,certain catalysts, additives, surfactants, cell openers, and otheradditives may include hydroxyl groups, and these sources of hydroxylgroups are also included in calculating the denominator of the Index.

As is known to those skilled in the art, the number of equivalents of afunctional group in a particular polymeric material or in a givenmolecule can be determined by the following equation:

$\begin{matrix}{{{No}.\mspace{14mu} {Equivalents}} = \frac{{{Wt}.\mspace{14mu} {of}}\mspace{14mu} {polymer}\mspace{14mu} {or}\mspace{14mu} {molecule}\mspace{14mu} (g)}{\begin{matrix}{{equivalent}\mspace{14mu} {weight}\mspace{14mu} {of}\mspace{14mu} {the}\mspace{14mu} {polymer}\mspace{14mu} {or}\mspace{14mu} {molecule}} \\\left( {g/{equivalent}} \right)\end{matrix}}} & (2)\end{matrix}$

For a given molecule bearing a particular functional group, theequivalent weight may be determined as follows:

$\begin{matrix}{{{Equivalent}\mspace{14mu} {Weight}} = \frac{\begin{matrix}{{{molecular}\mspace{14mu} {weight}\mspace{14mu} {of}\mspace{14mu} {functional}}{\mspace{11mu} \;}} \\{{group}\mspace{14mu} \left( {g\text{/}{mol}} \right)}\end{matrix}}{\begin{matrix}{{{number}\mspace{14mu} {of}\mspace{14mu} {occurrences}\mspace{14mu} {of}\mspace{14mu} {the}}{\mspace{11mu} \;}} \\{{functional}\mspace{14mu} {group}\mspace{14mu} {on}\mspace{14mu} {the}\mspace{14mu} {molecule}}\end{matrix}}} & (3)\end{matrix}$

Many commercially available polyisocyanates are mixtures of isocyanatemolecules, oligomers, and/or polymers and are characterized based ontheir percentage by weight of isocyanate functional groups (% NCO).Thus, the equivalent weight based on isocyanate groups can be calculatedas follows:

$\begin{matrix}{{{Equivalent}\mspace{14mu} {weight}} = \frac{{{molecular}\mspace{14mu} {weight}\mspace{14mu} {of}} - {NCO}}{\left( {\% \mspace{14mu} {{NCO}/100}} \right)}} & (4)\end{matrix}$

Where the molecular weight of −NCO is 42 g/mol. Many commerciallyavailable polyols are characterized by a “hydroxyl number” (“OH number”)which represents the number of milligrams of potassium hydroxideequivalent to the hydroxyl content of 1.0 gram of the polyol. For suchpolyols, the equivalent weight based on hydroxyl groups can becalculated as follows:

$\begin{matrix}{{{Equivalent}\mspace{14mu} {weight}} = \frac{\left( {56.1\mspace{14mu} g\mspace{14mu} {KOH}\text{/}{mol}} \right)\left( {1000\mspace{14mu} {mg}\text{/}g} \right)}{{OH}\mspace{14mu} {number}\mspace{14mu} \left( {{mg}\mspace{14mu} {KOH}\text{/}g\mspace{14mu} {polyol}} \right)}} & (5)\end{matrix}$

As indicated above, in certain illustrative formulations describedherein, water is provided and acts as a blowing agent. Water has twohydrogen atoms and is considered to be a di-functional molecule becauseone molecule of water consumes two (2) isocyanate groups. Thus, theequivalent weight of water is 18 (g/mol)/2=9 g/equivalent. Informulations involving multiple hydroxy-functional components, thenumber of equivalents of each component is calculated and summed toarrive at the denominator of the Index in equation (1) above.

In certain illustrative embodiments, the ratio of isocyanate equivalentsto hydroxyl equivalents (the Index) is adjusted to reduce the amount offree isocyanate monomer (e.g., MDI or TDI) that is volatilized duringthe polyurethane formation reaction. It is generally preferred that theIndex is less than 1.0. While lower Index values tend to reduce theamount of free isocyanate monomer, they also tend to undesirablyincrease the amount of water absorbed by the polymeric foam, owing tothe presence of additional, unreacted hydroxyl groups. Thus, in certainpreferred polymeric foam compositions, the Index ranges from about 0.80to less than 1.0. In more preferred compositions, the Index ranges fromabout 0.85 to about 0.95. In an especially preferred composition, theIndex ranges from about 0.90 to about 0.91.

A variety of different polyisocyanates may be used to preparepolyurethane foams of the type described herein. Suitablepolyisocyanates include organic polyisocyanates such as aromaticpolyisocyanates, aliphatic, cycloaliphatic, or araliphaticpolyisocyanates. Especially preferred are those polyisocyanates that areliquid at 25° C. Examples of suitable polyisocyanates include1,6-hexamethylenediisocyanate; isophorone diisocyanate; 1,4-cyclohexanediisocyanate; 4,4′-dicyclohexylmethane diisocyanate; 1,4-xylylenediisocyanate; 1,4-phenylene diisocyanate; 2,4-toluene diisocyanate;2,6-toluene diisocyanate; 4,4′-diphenylmethane diisocyanate (4,4′-MDI);2,4′-diphenylmethane diisocyanate (2,4′-MDI); polymethylenepolyphenylene polyisocyanates (crude, or polymeric, MDI); and1,5-naphthalene diisocyanate. Mixtures of these polyisocyanates can alsobe used. Moreover, polyisocyanate variants, for example polyisocyanatesthat have been modified by the introduction of urethane, allophanate,urea, biuret, carbodiimide, uretonimine, isocyanurate, and/oroxazolidone residues, can also be used.

In general, aromatic polyisocyanates are preferred. The most preferredaromatic polyisocyanates are 4,4′-MDI, 2,4′-MDI, polymeric MDI, MDIvariants, and mixtures of these. Isocyanate terminated prepolymers mayalso be employed, but are less preferred. Such prepolymers are generallyprepared by reacting a molar excess of polymeric or pure polyisocyanatewith one or more polyols. The polyols may include aminated polyols,imine or enamine modified polyols, polyether polyols, polyester polyolsor polyamines. Pseudoprepolymers, which are a mixture of isocyanateterminated prepolymer and one or more monomeric di or polyisocyanates,may also be used.

Toluene-2-4-diisocyanate, toluene-2-6-diisocyanate and mixtures thereofare generically referred to as “TDI.” Diphenylmethane-4,4′-diisocyanate(4,4′ methylene diphenyl diisocyanate),diphenylmethane-2,2′-diisocyanate (2,2′ methylene diphenyldiisocyanate), and diphenylmethane-2,4′-diisocyanate (2,4′ methylenediphenyl diisocyanate) and mixtures thereof are generically referred toas “MDI” herein. The 4,4′ isomer is referred to as “pure MDI”.

As is known to those skilled in the art, polyisocyanates can becharacterized based on a “functionality” that represents the averagenumber of isocyanate groups per molecule in the polyisocyanate. Thepolyisocyanates preferably have a number-averaged isocyanatefunctionality of from at least 1.8 to about 4.0 Especially preferredpolyisocyanates include MDI or TDI-based polyisocyanates having afunctionality of from about 2.0 to about 3.0, and more preferably fromabout 2.3 to about 2.9. As mentioned above, polyisocyanates may also becharacterized based on an isocyanate content (% NCO) that represents theamount of isocyanate functional groups that are present by weight. PureMDI has an isocyanate content of 33.6% by weight, and pure TDI has anisocyanate content of 48.2% by weight. Preferred polyisocyanates have anisocyanate content (by weight) that is above about twenty (20) percent.More preferred polyisocyanates have an isocyanate content of at leastabout twenty-five (25) percent by weight, and especially preferredpolyisocyanates have an isocyanate content of at least about 30 percentby weight. Commercially available polyisocyanates that are suitable foruse in the formulations described herein include those supplied byHuntsman Polyurethanes under the Rubinate® name. One exemplary MDI-basedpolyisocyanate is Rubinate® 8700. Rubinate® 8700 is a polymericdiphenylmethane diisocyanate comprising free MDI as well as some amountof polymerized and/or oligomerized MDI, which has a functionality ofapproximately 2.7 and an isocyanate content (by weight) of about 31.5percent.

A variety of polyols may be used to prepare polymeric foams inaccordance with this disclosure. Exemplary polyols includepolyhydroxyalkane polyols, polyoxyalkylene polyols, alkylene oxideadducts of polyhydroxyalkanes, alkylene oxide adducts of non-reducingsugars and sugar derivatives, alkylene oxide adducts of phosphorus andpolyphosphorus acids, alkylene oxide adducts of polyphenols and polyolsderived from natural oils, such as castor oil.

In a preferred polyurethane foam composition, two polyol components areused. The first polyol component is a sucrose-initiated polyol having afunctionality (i.e., average number of hydroxyl groups per molecule ofthe polyol) of from about 4 to about 5, and the second polyol componentis an amine-initiated polyol having a functionality of from about 2.5 toabout 3.5. One suitable sucrose-initiated polyol is Jeffol® SD 361,which is supplied by Huntsman Polyurethanes. Jeffol® SD 361 has ahydroxyl number of 360 and an average functionality of 4.4. Suitableamine-initiated polyols include Jeffol® A-630, which has a hydroxylnumber of 635 and an average functionality of 3.0.

As mentioned above, the polyurethane foams described herein are preparedby combining and reacting a “second component” comprising at least onepolyisocyanate with a “first component” that includes the at least onepolyol. In a preferred formulation, the amount of sucrose-initiatedpolyol generally ranges from about 50 percent to about 70 percent byweight of the first component and preferably ranges from about 55 toabout 65 percent by weight of the first component. The amount ofamine-initiated polyol ranges generally from about ten (10) to about 30percent by weight of the first component, and preferably ranges fromabout fifteen (15) to about twenty (20) percent by weight of the firstcomponent. This first component may also include several other types ofingredients used to adjust the properties of polyurethane foam, such ascross-linkers, chain extenders, cell openers, surfactants, and blowingagents.

The total amount of cross-linkers and chain extenders is preferablysufficient to cause cross-linking and chain extension to occur in thepolyurethane product. The total amount of cross-linkers and chainextenders ranges generally from about five (5) to about fifteen (15)percent by weight of the first component. Preferred cross-linkers andchain extenders include hydroxyl functional compounds, such as diols andtriols. In one preferred formulation, the first component used to formthe polyurethane foam comprises a diol that acts as both cross-linkerand chain extender and a triol cross linker. In an exemplaryformulation, the diol cross-linker/chain extender is polyethylene glycol400 (PEG 400) having a hydroxyl number ranging from about 267 to about295, such as Polyglykol 400, which is supplied by the ClariantCorporation. In an exemplary formulation, the triol cross-linker isglycerine (1,2,3 tri-hydroxy propane). The diol cross linker and chainextender is preferably present in an amount that is effective to causecross linking and chain extension to occur in the polyurethane. Thetriol cross linker is preferably present in an amount that is effectiveto cause cross-linking to occur in the polyurethane.

The first component may also comprise one or more catalysts, which arepreferably present in an amount ranging from about one to about ten (10)percent by weight of the first component. In one exemplary formulation,three catalysts are provided. As indicated previously, in the formationof polyurethane foams, isocyanate groups on the polyisocyanate reactwith hydroxyl groups on the polyols to form polyurethanes. Theisocyanate groups also react with water to form carbon dioxide. Thus,the use of multiple catalysts aids in selectively adjusting the relativekinetics of the polyurethane formation and carbon dioxide generationreactions. In one illustrative formulation, the first catalyst (whichmay be called a “balanced catalyst”) catalyzes the reaction ofpolyisocyanate and polyol and also catalyzes the gelation of thereaction product and the generation of carbon dioxide gas (i.e., itcatalyzes the “blow”). The second catalyst catalyzes the generation ofcarbon dioxide gas, and the third catalyst catalyzes gelation. Oneexemplary catalyst that may serve as the first catalyst is Polycat® 9, atertiary liquid amine catalyst supplied by Air Products and Chemicals,Inc. which is miscible in water and soluble in most polyols and organicsolvents. An exemplary catalyst that may serve as the second catalyst isJeffcat ZF-22, supplied by Huntsman Corporation. Jeffcat ZF-22 is amixture of 70 percent bis-(2-dimethylaminoethyl)ether and 30 percentdipropylene glycol. An exemplary catalyst that may serve as the third(gelling) catalyst is Fomrez UL 1, which is a dibutyltin mercaptidecatalyst supplied by Momentive Performance Materials of Wilton, Conn.The first catalyst is preferably present in an amount that is effectiveto catalyze the reaction of polyols with polyisocyanate, gelation, andblowing. In certain illustrative embodiments, the first catalyst ispresent in an amount ranging generally from about 0.2 to about 1.0percent by weight of the first (polyol-containing) component, and ispreferably present in an amount ranging from about 0.6 to about 0.7percent by weight. The second catalyst is preferably present in anamount that is effective to catalyze the generation of carbon dioxidegas from water and isocyanates. In certain illustrative embodiments, thesecond catalyst is present in an amount ranging from about 1.0 to about4.0 percent by weight of the first component, and preferably ranges fromabout 2.0 to about 3.0 percent by weight. The third catalyst ispreferably present in an amount that is effective to cause gelformation. In certain illustrative embodiments the third catalyst ispresent in an amount ranging from about 0.05 to about 0.2 percent byweight of the first component, and preferably ranges from about 0.1 toabout 0.2 percent by weight.

The first component may also comprise one or more cell opening compounds(cell-openers). Foams can be generally characterized as “open cell” or“closed cell” depending on whether the windows of adjacent cells areopen (i.e., such that the cells are in communication with one another)or closed. In certain illustrative embodiments, the polyurethane foamsdescribed herein generally have at least about 80 percent open cells. Incertain preferred embodiments, the foams have at least about 90 percentopen cells. In an especially preferred embodiment, at least about 95percent of the cells are open. The cell opening compounds facilitate theproduction of open cells. Exemplary cell openers include silicon-basedantifoamers, waxes, finely divided solids, liquid perfluorocarbons,paraffin oils and long chain fatty acids. If a cell opener is used, itis preferably present in an amount that is sufficient to provide thedesired percentage of open cells. In certain embodiments, the cellopener is present an amount that is generally less than one percent byweight of the first component, and which is preferably between about0.01 and about 0.1 percent by weight. One exemplary cell opener that maybe used is Ortegol® 501, a solution of organic polymers having ahydroxyl number of about 2 which is supplied by Evonik Industries.

To facilitate cell formation and stabilization, one or more surfactantsmay also be included in the first component of the polyurethaneformulation. Examples of surfactants include nonionic surfactants andwetting agents, such as those prepared by the sequential addition ofpropylene oxide and then ethylene oxide to propylene glycol, the solidor liquid organosilicones, polyethylene glycol ethers of long chainalcohols, tertiary amine or alkylolamine salt of long chain alkyl acidsulfate esters, alkyl sulfonic ester and alkyl arylsulfonic acids. Thetotal amount of surfactant is generally less than about two (2) percentby weight of the first component, with amounts ranging from about 1.0 toabout 1.5 percent being preferred. In certain preferred formulations, afirst polyether polydimethyl siloxane copolymer surfactant, and a secondnon-hydrolizable silicone copolymer surfactant are used. Exemplarypolyether polydimethyl siloxane copolymer surfactants include Tegostab®B8404, which is supplied by Evonik Industries. Exemplarynon-hydrolizable silicone copolymer surfactants include Niax SiliconeL-6900, which is supplied by Momentive Performance Materials.

Processes of making polyurethane foams from the first polyol-containingcomponent and second polyisocyanate-containing component discussed abovewill now be described. The polyol and polyisocyanate materials describedabove generally react quickly, on the order of less than a minute. Ingeneral, it is preferred to supply both the first polyol-containingcomponent and the second polyisocyanate-containing component as liquidsand to combine and apply them to the cavity or substrate of interestsubstantially contemporaneously, a process which may be referred to as“reaction injection molding” or “RIM.” If the first and secondcomponents are combined and applied using a RIM process, they arepreferably formulated with a viscosity that is sufficiently low to allowspray application. The combined components will preferably have areaction profile that achieves a sufficiently high viscosity to preventthe components from flowing away from or outside of the area to whichthe foam is to be applied. It is also preferable that the first andsecond components be formulated such that any volatilized residualmonomer (e.g., MDI or TDI) is released in sufficiently low amounts toavoid the need for ventilation equipment (hoods, down draft booths) orthe use of fresh air equipment. It should be noted that the residualmonomer present in the second polyisocyanate-containing componentbeneficially reduces the second component's viscosity, yielding aviscosity at 25° C. of from about 100 to about 300 cps, with a viscosityof from about 150 cps to about 200 cps being preferred. The lowerviscosity facilitates the pumping and spray application of the secondpolyisocyanate-containing component. Thus, in contrast with processesthat consume unreacted isocyanate monomers by forming a polyurethanepre-polymer before adding a blowing agent (e.g., water), the methodsdescribed herein provide polyol and polyisocyanate components that canreadily be pumped and combined to react as they are applied to a cavity,substrate, etc. In addition, the components described herein can beprocessed at a lower temperature as compared to those processesinvolving the formation of a pre-polymer.

An exemplary process 20 of preparing and applying polyurethane foams toa cavity to form, for example, structural reinforcing, sealing, and/oracoustic damping members is depicted in FIG. 1. In this exemplaryembodiment, the process equipment is provided in a portable form,allowing an operator to move it from location to location to apply thepolyurethane foam to the desired location. Reactant vessel 22 isprovided for containing the first polyol-containing component, andreactant vessel 30 is provided for containing the secondpolyisocyanate-containing component. The first polyol-containingcomponent preferably contains at least one polyol, such as thosedescribed above. If blowing agents (including water), cross-linkers,chain extenders, surfactants, catalysts, cell openers, or otheradditives are provided, they are preferably mixed with the polyols inreactant vessel 22.

Vessel 22 is fluidly connected to metering pump 24 and preheater 28.Preheater 28 is used to adjust the temperature of the firstpolyol-containing component and facilitates controlling the polyurethaneformation reaction temperature. Temperature gauge 26 provides anindication of the temperature of the first polyol-containing componentand may serve as an input to a feedback temperature controller thatadjusts the rate of heat supplied by preheater 28. Flexible conduit 38is preferably a hose or tube that connects the preheated first componentto application and mixing device 42.

Reactant vessel 30 contains the second polyisocyanate-containingcomponent, which preferably includes at least one polyisocyanate andresidual, free isocyanate monomer. As indicated above, other ingredientsused to prepare the polyurethane foam, such as blowing agents,catalysts, surfactants, cross-linkers, and chain extenders arepreferably not contained in reactant vessel 30, but are instead combinedwith the polyols in vessel 22. Vessel 30 is fluidly connected to pump 32and preheater 34. Preheater 34 is used to adjust the temperature of thesecond polyisocyanate-containing component and along with preheater 28facilitates controlling the polyurethane formation reaction temperature.Temperature gauge 36 provides an indication of the temperature of thesecond polyisocyanate containing component and may serve as an input toa feedback temperature controller that adjusts the rate of heat suppliedby preheater 34. Flexible conduit 40 is preferably a hose or tube thatconnects the preheated second component to application device 42.

The reaction temperature used to form polyurethane foams as describedherein generally ranges from about 100° F. to about 130° F. Preferredtemperatures range from about 105° F. to about 120° F. In one especiallypreferred embodiment, a reaction temperature of about 110° F. isemployed by adjusting preheaters 28 and 34 to provide respective outlettemperatures of about 110° F.

Application and mixing device 42 is preferably configured to turbulentlymix the first polyol-containing component and the secondpolyisocyanate-containing component and to deliver a mixed, controlledflow of the combined reactants to a cavity of interest. In a preferredembodiment, application device 42 is a spray gun such as the GX-15series of spray guns supplied by Graco, Inc. of Minneapolis, Minn. Asindicated in FIG. 1, application device 42 includes an internal mixvalve or head 44 that provides for impingement mixing of the firstpolyol-containing component and the second polyisocyanate-containingcomponent. The first polyol-containing component and the secondpolyisocyanate-containing component are preferably formulated to provideviscosities that are suitable for pumping the components from theirrespective vessels 22, 30 to application and mixing device 42 and toensure that the combined first and second components can be applied viaa spray process.

In the embodiment of FIG. 1, rigid structures 46 and 48 define a cavityin which a polyurethane foam member is installed. An acoustic foam ispreferred if rigid structures 46 and/or 48 will be subjected tovibration or other acoustic disturbances. An operator aligns applicationand mixing device 42 to discharge the combined first polyol-containingcomponent and second polyisocyanate containing component into port 50.The combined reactants react quickly to form a polyurethane foam 52 asthey are discharged from application and mixing device 42 into thecavity defined by structures 46 and 48. Structures 46 and 48 maycomprise a portion of a vehicle, such as an A-pillar or other areaswhere it is desirable to provide an acoustic foam, seal a cavity, and/orprovide structural reinforcement.

As mentioned above, the preparation of polyurethane foams as describedherein beneficially reduces the amount of volatilized free isocyanatemonomer that is emitted and thus can be performed without the use ofventilation equipment or fresh air. In certain preferred embodiments,the process of forming the polyurethane foams results in the emission ofless than 10 micrograms of free isocyanate monomer for every pound ofsolid foam that is formed. In a preferred embodiment, less than 0.5micrograms of free isocyanate monomer is released for every pound ofsolid foam that is formed. In one exemplary process, less than 0.45micrograms of free isocyanate monomer is released per pound of foam,while in another exemplary process, less than 0.40 micrograms isreleased per pound of foam.

The U.S. Occupational Safety and Health Administration has published astandard and test method governing the permissible levels of atmosphericMDI which may be released, OSHA Organic Method #47, which isincorporated by reference herein. In addition, certain vehiclemanufacturers use the “5 gallon can test” to determine the amount offree isocyanate released in the production of polyurethane foams. Inaccordance with the 5 gallon can test method, 300 grams of the combinedfirst polyol-containing component and second polyisocyanate-containingcomponent are simultaneously mixed and injected as a single shot into a5 gallon can in an amount sufficient to produce an expanded foam thatoccupies approximately one-half of the can's volume. A Tedlar bag isattached to the can to accommodate the displacement of gas due to theinjection of the foam. Immediately after injection of the first andsecond components, the injection port is sealed to provide a closedsystem. A 13 mm treated filter cassette prepared in accordance with OSHAOrganic Method #47 is provided which is in fluid communication with thevapor space in the can. The cassette traps the volatilized freeisocyanate that is emitted during the foam formation reaction. Vaporfrom the can passes through the filter cassette, and the filtered vaporis directed back into the can with an air pump. The sampling iscontinued for a period of 5-10 minutes. The test is repeated ten (10)times to collect ten (10) cassettes. The cassettes are then analyzed todetermine the amount (micrograms) of free isocyanate (e.g., MDI)captured by the cassette, and the results are averaged. One exemplarymethod of performing the cassette analysis is the high pressure liquidchromatography (“HPLC”) method outlined in OSHA Organic Method #47. Incertain preferred embodiments, the foams prepared herein will emit nomore than 0.3 micrograms of free isocyanate monomer as measured by the 5gallon can test. If the free rise density of the foam is 2.0 lb/cu.ft.this yields an emission of 0.45 micrograms of free isocyanate per poundof foam, assuming that the foam occupies one-half of the five galloncan's volume.

As mentioned previously, polyurethane foams may be characterized by adensity measure known as “free rise density.” In certain illustrativeembodiments of polyurethane foams of the type described herein, the freerise density ranges generally from about 1.0 to about 5.0 lb/cu. ft. Incertain preferred embodiments, the free rise density ranges from about2.0 to about 3.0 lb./cu. ft., and in more preferred embodiments the freerise density ranges from about 2.0 to about 2.2 lb./cu. ft. Free risedensity may be determined by weighing a cup of a pre-determined volume(e.g., 16 fluid oz. or 32 fluid oz.) and over-filling it with foam tocreate a crown that rises above the cup's rim. The foam is then fullycured for a period of about 15 minutes, and the crown is cut off toensure that the foam closely conforms to the cup volume. The cup isagain weighed with the foam in it, and the weight of the foam isdetermined by calculating the difference between the weight of thefoamed cup and the weight of the cup prior to foaming. The free risevolume is then determined by dividing the foam weight by the cup volume.To improve the accuracy of the method, a cup of the same model may bepre-weighed and filled to its rim with water, which has a density of 1g/cc. The cup may then be re-weighed. The true volume of the cup incubic centimeters may then be determined by subtracting the weight ofthe pre-weighed cup from the weight of the water-filled cup. Thepreviously calculated foam weight may then be divided by the true cupvolume to obtain the free rise density.

The foams described herein may also be characterized based on theirabsorption of water under certain reference conditions. As indicatedpreviously, increases in the ratio of isocyanate equivalents to hydroxylequivalents tend to increase the amount of free isocyanate monomer thatis volatilized during a foam forming operation. However, as the ratiodecreases, the number of unreacted hydroxyl groups present in the foamincreases. The unreacted hydroxyl groups will have a tendency to absorbwater, which can degrade the acoustic, sealing, and/or strengtheningfunction of the foam. In one exemplary water absorption test, the foamis subjected to a 50° C., 95% relative humidity environment for a periodof seven (7) days, and the weight of the foam is determined before andafter the seven (7) day period. The percentage increase in the weight ofthe foam is then calculated. Using this water absorption test method,the foams described herein will generally have a water absorption ofless than about 30 percent, preferably, less than about ten (10)percent, and more preferably less than about five (5) percent. In oneespecially preferred exemplary, the polyurethane foam has a waterabsorption of about two (2) percent.

In certain exemplary processes, it is preferable that the firstpolyol-containing component and the second polyisocyanate-containingcomponent begin to foam quickly to provide an initial sag resistance asthe polyurethane formation reaction proceeds. One measure of therapidity of foaming is known as “cream time,” which is defined as theelapsed time between the dispensing of the firstpolyisocyanate-containing component and second polyol-containingcomponent and the moment when the combined components start to rise asdetected by visual observation. The formulations and processes describedherein will yield foams with a cream time that is generally less thanabout ten (10) seconds, with cream times of less than about five (5)seconds and less than about one (1) second being more preferred andespecially preferred, respectively.

In certain exemplary processes, it is preferable that the firstpolyol-containing component and the second polyisocyanate-containingcomponent react and gel quickly to ensure that the foam remainssubstantially contained within the cavity or on the substrate ofinterest. One measure that is useful for characterizing foams is knownas the “gel time.” One exemplary method of determining gel timecomprises dispensing a fixed mass (e.g., 60 g) of foam into a paper cup.Immediately following the dispensing step, the edge of a wooden tonguedepressor is repeatedly contacted with the expanding foam surface. Oncea string of material is formed from the combined first polyisocyanatecomponent and the second polyol-containing component, the elapsed timeis recorded. The process is preferably repeated several times, and thegel time is calculated as the average elapsed time between thedispensing of the first polyisocyanate-containing component and secondpolyol-containing component and the formation of a string of materialfrom the combined components. The foams prepared in the manner describedexhibit gel times that are generally from about two (2) to about ten(10) seconds. Gel times of from three (3) to about eight (5) seconds arepreferred, and a gel time of about four (4) seconds is more preferred.

Example

An exemplary polyurethane foam composition and process of making thefoam will now be described. The exemplary foam has a ratio of isocyanateequivalents to hydroxyl equivalents (i.e., an Index) of 0.91. 100 g of afirst polyol-containing component is prepared by combining theingredients listed in Table 1.

TABLE 1 Wt. —OH Equiv. No. Component Description (g) No. Wt. (g) Equiv.Jeffol ® SD-361 Sucrose-initiated polyol 62.08 360 155.83 0.3984Jeffol ® A-630 Amine-initiated polyol 17.74 635 88.34 0.2008 Polyglykol400 PEG 400 cross- 8.87 281 200 0.0444 linker/chain extender Glycerine1,2,3 tri-hydroxy propane 3.10 30.7 .1010 cross-linker Polycat ® 9Tertiary amine catalyst 0.67 n/a n/a 0 Fomrez ® UL-1 Dibutyltinmercaptide 0.13 n/a n/a 0 gelling catalyst Jeffcat ZF-22 70% bis (2-2.66 251 223 0.0120 dimethylaminoethyl)ether/ 30% dipropylene glycol,blow catalyst Tegostab ® B8404 Polyether polydimethyl- 0.89 n/a n/a 0siloxane copolymer surfactant Ortegol ® 501 organic polymer solution0.09  2 28050 0 cell opener Niax L-6900 Non-hydrolizable silicone 0.22 40 1403 0 copolymer surfactant Water Blowing agent 3.55 9 0.3944 TOTAL100 1.151

The second polyisocyanate containing component comprises 140 g ofRubinate® 8700 polymeric diphenylmethane diisocyanate, which alsoincludes free methylene diphenyl diisocyanate and has an isocyanatecontent of 31.5 percent by weight. The equivalent weight of Rubinate®8700 is 133 g/eq. Thus, 140 g of Rubinate® 8700 yields 1.05 equivalents,and the Index is 1.05/1.151=0.91.

The first and second components are preheated to a temperature of about110° F. and are combined in an application and mixing device such asspray gun 42 depicted in FIG. 1. The components are then sprayed into acavity of a structure and allowed to react and cure, yielding asubstantially rigid foam. The free MDI that is emitted during theprocess is less than 0.45 micrograms/lb. foam, and the free rise densityis in the range of about 2.0 to 2.2 lb./cu. ft. The water absorptionbased on exposure to 95% relative humidity using the test methodpreviously described is about two (2) percent. The foam has a cream timeof less than one (1) second, a gel time of about four (4) seconds andshows excellent sag resistance.

Referring to FIG. 2, design of experiment data is provided for thefollowing modified version of the foam formulation provided in Table 1.

TABLE 2 Component Description Wt. % Jeffol ® SD-361 Sucrose-initiatedpolyol 63.56 Jeffol ® A-630 Amine-initiated polyol 18.16 Polyglykol 400PEG 400 cross-linker/chain extender 9.08 Glycerine 1,2,3 tri-hydroxypropane cross-linker 3.18 Polycat ® 9 Tertiary amine catalyst 0.68Fomrez ® UL-1 Dibutyltin mercaptide gelling catalyst 0.03 Jeffcat ZF-2270% bis (2-dimethylaminoethyl)ether/30% 0.64 dipropylene glycol, blowcatalyst Tegostab ® B8404 Polyether polydimethyl-siloxane 0.91 copolymersurfactant Ortegol ® 501 organic polymer solution cell opener 0.14 WaterBlowing agent 3.63 TOTAL 100

The x-axis of FIG. 2 is a plot of the Index, i.e., the ratio ofisocyanate equivalents to hydroxyl equivalents (including water). Thecenter point represents an Index of 0.90, and the end-points representIndices of 0.85 and 0.95. The y-axis is a plot of reaction temperature,with isotherms being represented as diagonal lines. The z-axis is a plotof free MDI emitted during foam formation based on the 5 gallon can testprocedure described previously. As FIG. 2 indicates, as the Indexincreases, the free MDI that is volatilized increases because fewerhydroxyl groups are available to react with free MDI. As the reactiontemperature increases, the amount of free MDI that is volatilized alsoincreases due to the increased vapor pressure of the MDI. Thus, theindex and/or reaction temperature can be varied as desired to obtain thedesired degree of volatilized free MDI.

Preferred embodiments have been disclosed. A person of ordinary skill inthe art would realize, however, that certain modifications would comewithin the teachings of this Invention, and the following claims shouldbe studied to determine the true scope and content of the invention. Inaddition, the methods and structures of representative embodiments canbe incorporated in the form of a variety of embodiments, only a few ofwhich are described herein. It will be apparent to the artisan thatother embodiments exist that does not depart from the spirit of theinvention. Thus, the described embodiments are illustrative and shouldnot be construed as restrictive.

1-28. (canceled)
 29. A method of making polyurethane foam, comprising:reacting a first component comprising at least one polyol and a secondcomponent comprising at least one polyisocyanate to form a reactionproduct, wherein the ratio of the number of isocyanate equivalents inthe second component to the number of hydroxyl equivalents in the firstcomponent is less than 1.0, and the at least one polyol comprises anamine-initiated poly (alkylene oxide) polyol, a polyhydricether-initiated poly (alkylene oxide) polyol, and acarbohydrate-initiated poly (alkylene oxide) polyol, and theamine-initiated poly (alkylene oxide) polyol is present in an amountfrom about 10 percent to about 30 percent by weight of the firstcomponent and wherein the reaction product is a foam that has a weight,and when the foam is subjected to 95 percent relative humidity for aperiod of 7 days at a temperature of about 50° C., the foam absorbs anamount of water that is less than about 30 percent of the weight of thefoam.
 30. The method of claim 29 further comprising maintaining areaction temperature between about 100° F. and about 130° F.
 31. Amethod of reducing NVH expected to experienced by a substrate,comprising mixing a first component comprising at least one polyol witha second component comprising at least one polyisocyanate therebycausing a reaction to form a polyurethane foam; and applying the mixtureto the substrate that is expected to be exposed to NVH; wherein theratio of the number of isocyanate equivalents in the second component tothe number of hydroxyl equivalents in the first component is less than1.0, and the at least one polyol comprises an amine-initiated poly(alkylene oxide) polyol, a polyhydric ether-initiated poly (alkyleneoxide) polyol, and a carbohydrate-initiated poly (alkylene oxide)polyol, and the amine-initiated poly (alkylene oxide) polyol is presentin an amount from about 10 percent to about 30 percent by weight of thefirst component and wherein the polyurethane foam has a weight, and whenthe polyurethane foam is subjected to 95 percent relative humidity for aperiod of 7 days at a temperature of about 50° C., the polyurethane foamabsorbs an amount of water that is less than about 30 percent of theweight of the foam.
 32. The method of claim 31 wherein mixing andapplying occurs substantially contemporaneously.
 33. The method of claim31 wherein applying comprises spraying the mixture on the substrate. 34.The method of claim 31 wherein the substrate is a metal surface in acavity of an automobile.